One major difficulty met in organic synthesis of epoxides stems from the reactivity of the epoxy group. Under a wide variety of conditions, epoxides will react with solvents and a large number of organic functional groups, one consequence being that introduction of an epoxy group into a complex, polyfunctional organic molecule can be an exceedingly difficult if not an impossible task.
One example of this kind relates to carbohydrate molecules carrying an epoxy group in the glucosidic aglycone, c.f. formula I. ##STR1##
Due to the presence in such molecules of many reactive groups, the low solubility of the compounds in most organic solvents and the fragile character of the molecules it is a difficult and often quite lengthy task to prepare such compounds by organic synthesis. One example described by J. E. G. Barnett and A. Ralph in Carbohydr. Res. 17 (1971), 231, relates to synthesis of 2,3-epoxypropyl-.beta.-D-glucopyranoside of formula II. ##STR2## Synthesis of sugar molecules carrying an epoxy group comprises a rather long sequence of synthetic steps from readily available starting materials.
In recent years there has been a growing awareness in regard to the potential of enzymes as organic catalysts. As these catalysts are unique in many respects they are potentially very useful in organic synthesis. For example, the enzymes open up the possibility of performing organic reactions under exceedingly mild conditions, and they are often substrate selective, whereby for example selective conversion of a single group among several chemically very similar groups in organic molecules or synthesis of optically pure organic components from racemic starting materials is made possible.
One group of enzymes which have attracted some interest as organic catalysts are enzymes capable of splitting bonds at the C-1 position (aldoses) or C-2 position (ketoses) of a carbohydrate. These enzymes have attracted the interest of organic chemists due to the possibility of performing some chemical reactions at the enzymatic cleaving sites.
The use of .beta.-galactosidases for synthesis of galactosides illustrates how enzymes, which are able to split bonds at the C-1 position (aldoses) or C-2 position (ketoses) of carbohydrates can be utilized for organic synthesis. Thus, in J. Biol. Chem. 248 (1973), 6571-6574, T. J. Silhavy and co-workers describe how (2R)-glyceryl-.beta.-D-galactopyranoside can be synthesised from lactose and isopropylideneglycerol which are condensed to the corresponding galactoside by exposure to the .beta.-galactosidase produced by E. coli and subsequently split by acid catalysis to the desired products. Similarly, T. Satoh and co-workers describe in Chem. Pharm. Bull. 32 (1984), 1183-1187, the use of lactase from Kleuromyces fragilis for synthesis of a series of galactosides. These workers make use of aryl glucosides as starting material for an enzyme catalysed exchange reaction with compound ROH (wherein R was alkyl) for synthesizing a series of alkyl glucosides. It appears from this publication that principally the same reaction can be carried out with widely differing radicals R, and in this regard this prior art reaction may be considered antecedent to the method according to the invention.